UID Changeable cards are used to duplicate Mifare Classic 1K access cards.  Whilst generally it is best practice to use unique Mifare Classic 14443A cards for each user, there are some instances where you may wish to clone a card and have multiple cards with the same UID and data.  For example access control with few users with no user having the ability to add new cards into the system.  Or for access control that has a user limit which has been reached.  All three types of cards can be programmed with the Proxmark3, ACR122U or iCopy-XS devices.

IMPORTANT: There are three different types of cards that you can choose from:

Type 1: Normal GEN1 UID Changeable Cards:

• All blocks (including Block 0) can be re-written multiple times
• Use ProxMark3 (Magic Chinese Guy function) or libnfc to change UID.
• Uses “backdoor” technique to change/rewrite UID.
• UID can be changed multiple times.
• Not suitable for MCT on Android (Mifare Classic Tool)
• Answers to Chinese magic backdoor commands (GEN 1a): YES

The UID of MIFARE Classic® Compatible 1K Direct Write UID Tags is comprised of two parts: the UID itself, and the BCC. The BCC is a checksum value calculated from the UID. If the BCC is incorrect, tag will be rejected by the reader.

Most RFID tools, such as the Proxmark, LibNFC, MCT etc automatically calculate the BCC when the UID is modified. If you are modifying the UID by hand, it is vital that the BCC is correctly calculated.

KSEC cannot provide support or refunds under any circumstances for cards that were ‘bricked’ due to incorrect UID/BCC configuration.